The present invention relates to a tip turbine engine, and more particularly to peripheral combustor for a tip turbine engine.
An aircraft gas turbine engine of the conventional turbofan type generally includes a forward bypass fan and a low pressure compressor, a middle core engine, and an aft low pressure turbine, all located along a common longitudinal axis. A high pressure compressor and a high pressure turbine of the core engine are interconnected by a high spool shaft. The high pressure compressor is rotatably driven to compress air entering the core engine to a relatively high pressure. This high pressure air is then mixed with fuel in a combustor, where it is ignited to form a high energy gas stream. The gas stream flows axially aft to rotatably drive the high pressure turbine, which rotatably drives the high pressure compressor via the high spool shaft. The gas stream leaving the high pressure turbine is expanded through the low pressure turbine, which rotatably drives the bypass fan and low pressure compressor via a low spool shaft.
Although highly efficient, conventional turbofan engines operate in an axial flow relationship. The axial flow relationship results in a relatively complicated elongated engine structure of considerable length relative to the engine diameter. This elongated shape may complicate or prevent packaging of the engine into particular applications.
A recent development in gas turbine engines is the tip turbine engine. Tip turbine engines locate an axial compressor forward of a bypass fan which includes hollow fan blades that receive airflow from the axial compressor therethrough such that the hollow fan blades operate as a centrifugal compressor. Compressed core airflow from the hollow fan blades is mixed with fuel in an annular combustor, where it is ignited to form a high energy gas stream which drives the turbine that is integrated onto the tips of the hollow bypass fan blades for rotation therewith as generally disclosed in U.S. Patent Application Publication Nos.: 20030192303; 20030192304; and 20040025490. The tip turbine engine provides a thrust-to-weight ratio equivalent to or greater than conventional turbofan engines of the same class, but within a package of significantly shorter length.
In the known tip turbine engines, the core airflow flows radially outwardly from the radial outer ends of the hollow fan blades into the combustor, which is mounted about the periphery of the fan. A fuel injector aft of the fan delivers fuel into the combustor where it is ignited. The high-energy gas stream is then directed axially forward in the combustor, then redirected radially inward and then turned once again axially rearward to pass through turbine blades between the fan blades to rotatably drive the fan. One drawback of this arrangement is that mounting the combustor about the periphery of the fan increases the overall diameter of the known tip turbine engine. Additionally, in the known tip turbine engines, the compressed airflow from the hollow fan blades exits directly into the combustor. A lack of diffusion between the centrifugal compressor and the combustor causes a large loss in efficiency.